<title>Input and Output</title> 
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<h1>Input and Output</h1> 
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<p>
The C language does not have any I/O capability! You can access 
files and devices via two groups of functions, these can be split
as shown below.<p>

<ul>
<li><a href=#low>Low level.</a>
<li><a href=#ansi>ANSI.</a>
</ul>
<a name=low>
<h2>Low Level I/O</h2>

Low level functions provide direct access to files and devices. If you
only need file read and write you should use the 
<a href=#ansi>ANSI</a> functions as your code will remain portable.
If you want to access things like, serial ports, virtual memory and 
tape drives, low level I/O is for you.<p>

Low level functions reference files by a 
<a href=../glossary.html#filedes>file descriptor</a>, this descriptor 
is created with the <a href=../FUNCTIONS/open.html>open</a> function and
can be referenced by functions like:<p>
<a href=../FUNCTIONS/close.html>close</a><br>
<a href=../FUNCTIONS/read.html>read</a><br>
<a href=../FUNCTIONS/write.html>write</a><br>
mmap - Memory map (Not supported on Linux).<br>
<a href=../MAN/ioctl.htm>ioctl</a> I/O control.<p>

Three 'file descripters' are opened automatically when your program runs.
These are:
<pre>
	File		Default
	Desc	Name	device
	----    ----	------
	0	<a href=stdfiles.html>stdin</a>	Keyboard
	1	<a href=stdfiles.html>stdout</a>	Screen
	2	<a href=stdfiles.html>stderr</a>	Screen
</pre>

If you want to use these 'file descriptors', you do not have to issue an 
'open'.


<a name=ansi>
<h2>ANSI standard functions</h2>

These functions are defined in the 
<a href=../FUNCTIONS/function.ref.html#stdio>stdio.h</a> header.

The important thing to remember with these functions is the data 
is presented in a consistant manor across all platforms. A record
is considered to be 0 or more characters followed by a 
<a href=../FUNCTIONS/escape.html>newline</a> character.
If the actual (physical) record is terminated in some other way, the 
functions will perform the conversion for you.
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<address><a href=../../address.html>Martin Leslie</a> 
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